1. Field of the Invention
This invention relates to fibers to be bonded to a rubber composition and, more particularly, to fibers that are treated to cause effective adherence of the fibers to a rubber composition. The invention is also directed to a power transmission belt with the treated fibers incorporated therein.
2. Background Art
There has been an ongoing trend to design and produce energy-efficient automobiles. Typically, this efficiency is attributable to the compaction of these cars which is made possible, in part, by a reduction in the size of the engine compartments. This often results in a higher temperature environment in the compartments. As a result, power transmission belts used in the automobiles are often subjected to high operating temperatures.
Conventional power transmission belts are commonly made from natural rubber, styrene-butadiene rubber, and chloroprene rubber. The compression sections of the belts are prone to cracking at these high temperatures at a relatively early stage in the intended belt life.
Recently, hydrogenated nitrile rubbers have been developed as a heat-resistant polymer for use in power transmission belts, including V-belts, V-ribbed belts and toothed belts. A rubber composition with hydrogenated nitrile rubber and a metal salt of an unsaturated carboxylic acid has also been used in an elastic portion of the power transmission belts. Efforts are ongoing to improve the adhesion of fiber, load carrying cords to hydrogenated nitrile rubber.
As an example, Japanese Patent Publication (JP-B)Sho-60-24 131 discloses treatment of fiber cords with an RFL liquid that includes a carboxyl group having acrylonitrile-butadiene rubber latex.
JP-B Hei-6-41528 discloses treating cords with an epoxy compound or an isocyanate compound in a first step, treating the cords with an RFL liquid in a second step, and treating the cords with a rubber paste made from a rubber composition and a rubber chloride dissolved in a solvent in a third step.
Treating fiber cords with an RFL liquid that includes a carboxyl group having acrylonitrile-butadiene rubber latex improves adhesion of the fiber cords to hydrogenated nitrile rubber. However, it has been found through testing that, when power transmission belts incorporating the process cords are repeatedly fatigued during operation, the cords tend to peel off from the adhesion rubber layer at the interface therebetween at an early stage, demonstrating that the adhesion between the cords and rubber is unsatisfactory.
The adhesive composition consisting of an active compound, an RFL liquid, and an halogen-containing polymer has the drawback that use of the halogen-containing polymer must be limited to address environmental concerns.
The method described in JP-B Hei-6-41528 also has the drawback that the use of rubber chloride must be limited for environmental reasons. Further, the availability of this composition in the future is uncertain.
In one form, the invention is directed to processed fiber for bonding to a rubber composition. The processed fiber consists of unprocessed fiber treated with a) a first processing liquid having at least one of an isocyanate compound and an epoxy compound, b) a second processing liquid having RFL that includes at least one rubber latex selected from acrylonitrile-butadiene rubber latex and hydrogenated nitrile rubber latex, and c) a third processing liquid having rubber paste including acrylonitrile-butadiene rubber composition dissolved in a solvent and an isocyanate compound. The weight ratio of the isocyanate compound to the acrylonitrile-butadiene rubber composition is from 1/1 to 1/3. The third processing liquid has a solid content of from 3-7%.
The fiber may be treated with the second processing liquid after being treated with the first processing liquid, with the fiber being treated with the third processing liquid after being treated with the second processing liquid.
The fiber may be at least one of polyethylene terephthalate fiber (PET), polyethylene naphthalate fiber (PEN), aramid fiber, and 6-nylon.
The fiber may be treated with the first processing liquid for 0.5-30 seconds and thereafter heated at a temperature of 150-190xc2x0 C. for from 2-5 minutes.
The RFL processing liquid may be a mixture of resorcinol and formalin with rubber latex in which the molar ratio of resorcinol to formalin is from 3/1 to 1/3.
The RFL processing liquid may be prepared by mixing a precondensate of resorcinol and formalin with rubber latex so that the resin content is from 5-100 parts by weight relative to 100 parts by weight of rubber content in the rubber latex and so that the solid content of the RFL processing liquid is from 5-40%.
The fiber may be treated with the second processing liquid at 5-40xc2x0 C. for 0.5-30 seconds and thereafter heated at a temperature of 220-250xc2x0 C. for from 1-3 minutes.
The fiber may be treated with the third processing liquid at 5-40xc2x0 C. for 0.5-30 seconds and thereafter heated at a temperature of from 140-180xc2x0 C. for from 3-7 minutes.
The isocyanate compound in the first processing liquid may include one of 4,4xe2x80x2-diphenylmethane diisocyanate, toluene 2,4-diisocyanate, polymethylene polyphenyl-diisocyanate, hexamethylene diisocyanate, polyaryl polyisocyanate, and blocked polyisocyanate prepared by reacting an isocyanate compound with a blocking agent.
The acrylonitrile-butadiene rubber composition in the third processing liquid may include acrylonitrile-butadiene rubber with at least one of a reinforcing agent, a filler, a softener, an anti-aging agent, and a vulcanization agent added thereto.
The epoxy compound in the first processing liquid may include at least one of the reaction product of at least one of polyalcohol and polyalkylene glycol, a halogen-containing epoxy compound, and a reaction product of polyphenol.
The epoxy compound in the first processing liquid may be mixed with an organic solvent.
The invention is also directed to a power transmission belt having an endless body with a length and fiber embedded in the endless body, with the fiber having the composition as described above.
The fiber may define a cord which extends lengthwise in the body.
In one form, the body has a cushion layer made from rubber and the cord is embedded in the cushion layer and extends endlessly within the body.
The compressible rubber may be made from alkylated chlorosulfonated polyethylene with a low density polyethylene that has a linear molecular structure and is chlorosulfonated to have a chlorine content of from 15-35% by weight and a sulfur content of from 0.5-2.5% by weight.
The power transmission belt may be a V-belt or a V-ribbed belt.
The power transmission belt may be a toothed belt having teeth spaced from each other lengthwise of the body, with the body having an inside layer in which the teeth are formed, and a back layer, with the cord being embedded in the back layer.
In one form, the body has a compression section with rubber that includes at least one of alkylated chlorosulfonated polyethylene (ACSM), hydrogenated nitrile rubber (H-NBR), nitrile-butadiene rubber (NBR), chloroprene rubber (CR), and chlorosulfonated polyethylene rubber (CSM).
The body may have a cushion rubber layer in which the cord is embedded with the cushion rubber layer being made from a hydrogenated nitrile rubber composition.
The hydrogenated rubber composition may include hydrogenated nitrile rubber to which is added at least one of a reinforcing agent, a filler, a softener, an anti-aging agent, a vulcanization promoter, and a vulcanizing agent.